Use of the telephone as a social and business instrument has exponentially grown over the past 100 years. The widespread acceptance of the telephone and its uses have spurred industry to create many innovations to facilitate call completion and enhance telephone services. Today's telephone user community is sophisticated in the use of telecommunications equipment and demands faster connections, more services, and better integration with computer applications to assist in streamlining their business operations.
The Public Switched Telephone Network (PSTN) has evolved to a highly automated computer-controlled switched network which permits callers to place calls to practically anywhere in the world. In this document use of the term PSTN is intended to refer to any intelligent switched telephone network.
Much of the PSTN is now referred to as the Advanced Intelligent Network (AIN). In AIN, standardized "triggers" embedded in the fabric of the network switching nodes permit call requests to trigger database queries for seeking call routing information. After call routing information is returned from a queried database, the call is connected through the network using standard procedures.
Although the AIN is a high-speed multifaceted network which provides a vast array of automated telephone services, service development in the AIN is channelled by the AIN call model. In the AIN new service development is accomplished using Service Creation Environments to create service logic programs that are executed by Intelligent Service Control Points (ISCPs), which are databases that respond to switch queries initiated by the AIN triggers. In the AIN call model the opportunities for initiating routing decisions are essentially limited to the trigger points embedded in the network switch fabric. Although the services offered in the PSTN are constantly being expanded and enhanced, new services are now routinely developed within the context of the AIN call model.
An example of one such new service is taught in U.S. Pat. No. 5,377,186 that issued Dec. 27, 1994 to Wegner et al. It provides a system and method for retrieving enhanced subscriber services from a database and delivering those services to subscribers of the PSTN without requiring the upgrading of local switches to operate with Transaction Capabilities Application Part/Advanced Intelligent Network (TCAP/AIN) communications protocol. A plurality of local switches that are connected to an Advanced Intelligent Network (AIN) are enabled to provide subscribers with access to the network. This is accomplished using at least one Virtual Service Switching Point (ViSSP) within the AIN for storing a database of enhanced subscriber services. The local switches or tandem switches to which they are linked may retrieve the enhanced subscriber services from the ViSSP utilizing the Integrated Services Digital Network User Part (ISUP) of SS7 call set-up protocol. While the patent teaches the use of a virtual service switching point to expand AIN capabilities into local switches without expensive local switch upgrades, the use of the ViSSP is limited to use in accordance with the AIN call model described above.
The computer communications industry and the telecommunications industries are beginning to merge, but there has always been a measure of difficulty with the integration of the two. The PSTN has been perceived by those in computer communications as a closed architecture, encouraging computer vendors to displace the PSTN by creating overlay networks which avoid capitalizing on any more than core PSTN functionality.
Call routing using an overlay network requires many additional connections to the PSTN for both access and egress. Besides, routing within the PSTN from overlay networks often leaves connections established in nodes which are redundant to the call path. In overlay networks where there are limited connection points to the PSTN, calls can be routed over significant distances even though a call may complete on a network switching node where it originated. To address this problem, the telephone industry has endorsed the solution of release link trunk functionality for subsequent routing or rerouting of calls. The release link trunk functionality can reside in either the PSTN or in an overlay network, but the release link feature can only reside within a network switching node. The release link feature permits data messaging, usually SS7 ISUP messaging, to release a call back to the call set-up point, where rerouting can be performed to redirect the call. This feature is in wide use in the telecommunications industry today. Although the release link feature resolves some of the problems associated with redundant connections in the call path, the fact it is switching node resident is a significant drawback. Switch development and differences in proprietary protocols limit the use and availability of release link features. The development of new features for telephone switching nodes generally requires many months and involves considerable expense. Switch vendors therefore prioritize feature implementation based on aggregate demand, frequently placing service providers in a position of waiting for feature implementation. Adjunct solutions such as Intelligent Peripherals (IP) are therefore often sought. The intelligent peripherals provide resource management of devices such as voice response units, voice announcers and DMTF units for call-activated services. IPs are not seen in the signaling network, however, so they are not enabled to directly control call processes.
Other innovative workarounds have been inspired by the unique requirements of call centers, for example. In session activation, transfer and connect, line transfer and other features have been implemented in the PSTN using novel solutions. To date, however, service developers have not really leveraged the call routing power resident in the PSTN.